Thrombosis, or blood clot formation, is the most common cause of hemodialysis access graft failure. Graft thrombosis usually results from venous flow obstruction, or stenosis. The location of the stenosis is most commonly found at the graft-vein anastomosis. A narrowing at this area causes a slow down or obstruction of blood flow resulting in the formation of the thrombus within the graft. Venous stenosis is present in over eighty-five percent of clotted grafts. The underlying venous anastamotic stenosis must be corrected in order to avoid recurrence of the thrombus. The venous stenosis is usually treated with balloon angioplasty after the graft has been cleared of the thrombus.
Treatment options for thrombosed grafts include surgical thrombectomy, graft replacement, or percutaneous endovascular thrombolysis. Percutaneous thrombolysis is the least invasive treatment option and has rapidly become the preferred method of treatment at most institutions. It can be accomplished using mechanical thrombectomy devices that macerate the clot or by using a thrombolytic agent to dissolve the clot. Mechanical thrombectomy devices are expensive and often require capital investment. Thrombolytic agents provide a less expensive treatment option.
Tissue plasminogen activators, also known as TPA, are one of the most commonly used thrombolytic agents for clearing dialysis grafts. The drug is introduced into the clotted graft via an infusion catheter or a needle. TPA has a high affinity and specificity for fibrin, a major component of blood clots. It acts upon the clot by binding to the surface and dissolving it by an enzymatic reaction. Time until clot dissolution is dependent on the length and size of the clot, the amount of drug delivered, and method used for drug delivery.
With the “lyse and wait” technique of thrombolysis, TPA or other thrombolytic agent such as urokinase or retaplase is delivered to the graft by a small gauge needle or an infusion catheter. Manual compression is applied to the graft anastomoses during drug administration to ensure targeted drug delivery is restricted to the graft. The procedure is performed without the aid of fluoroscopic guidance. The therapeutic action of the lytic agent typically takes at least one hour depending on the effective distribution of the lytic agent. After clot dissolution, the patient typically is brought into the angiographic suite for fluoroscopic imaging of the graft to identify and visualize residual venous stenosis. Angioplasty of the stenosed segment can then be performed.